Buffer-machine for alternating-current systems.



A. SCHEFIBIUS.

BUF FER MACHINE FOR ALTERNATING CURRENT SYSTEMS. APPLICATION min JUNE21.1908.

1,167,1 19. Patented Jan. 4, 1916.

s f g 9 i? Z yzfzw v UNITED .sTAtrns PATENT OFFICE. I

ARTHUR SCHERBIUS, OF BADEN, SWITZERLAND, ASSIGNOR TOGENER AL ELECTRICCOMTANY, A CORPORATION OF NEW YORK.

BUFFER-MACHINE FOR. ALTERNATING-CURRENT SYSTEMS.

Specification of'Iletters Patent.

Patented Jan. 4, 1916.

Application filed June 27, 1908. Serial No. 440,694. i

To all whom it mag/concern Be it known that I, ARTHUR ScHnRBiUs, acitizen "of the Swiss Confederation, and resident of Baden, Switzerland,have invented certain new and useful Improvements in BuffepMachines forAlternating Current Systems, of which the following is a specification.

This invention relates to butler-sets designed-for use in'cennectionwith' power energy will be transformed to mechanical energy and storedin the fly-wheel, while when the load on the system is heavy aretransformation will take place and the fly.-

wheel give up its energy and return electrical energy to the system;These arrangements depend on the characteristic of anasynchronousmachine that it will operate as either a motor or generater. All such schemes must, however, be so designed that the frequency ofthe currentreturned is substantially the same as that of the system, butwe know that in order that the fly-wheel shall give upmechanical'energy, a decrease in its speed is necessary, and such achange in speed would mean a change in fre quency. a oided and theresult accomplished by changing the connections of the primary of theasynchronous machine so that the number of poles is changed, or by usingtwo machines which may be cormectcd in cascade,

so that in eithcr'casc the synchronous speed will be lowered andt.hc-fly-wheclwill be able to drive the set above synchronism and causethe machine to act as a generator and deliver energy of the properfrequency. 'lhcsc arrangements lune the disadvantage, howevclz that tho.change from motor to goncrator action is accompanied by a considcra lilcshock, or else a. substantial part of the energy must hr consumed inIt'SlSttllKitH to avoid these shocks Heretofore the difficulty has been0f distribution, and returning it again to the system with theproperfrequency at all speeds,flwhich shall operate ellie'iently and withoutsubstantial shocks. To this end I provide a, buffer set comprising aflywheel,

an asynchronous -maehine ,usually constructed as-an induction inotor'anda commutator machine mounted on the same shaft, thecommuted winding ofthe commutator machine being connected to the secondary winding of theinduction motor, the

primary winding ofwhich is connected to themains, so that the butter setat. times takes energy from the line and at times gives I energy to theline.

The accompanylng'drawing shows d agrammatically by Way of example onearrangement according to the present invention' in which the operationof the buffer machine is controlled automatically.

Infthe form of the invention illustrated in commutator machine'c'may'be' controlled in any suitable manner to cause the induction motorto work as a motor or generator and for example may be excitedbywindings g from its own terminals, the number of which windings may becontrolled by a conductive contact deviceo mountcdon one arm of a leverlathe other arm of which the drawing a three phase system is shown maybe connected with a solenoid core i operable by the solenoid la fed fromthe mains-l. Controlling a commutator machine by varying the number ofits acting field coils is known "and forms no part of the presentinvention; v

The buffer arrangemcnt is connected to the system by the leads 1:, whichjoin the mains l to the primary winding of the induction motor I). Theoperation of such an arrangcuu-nt may be considered as follows: Assumethat theswitrhcs of the load t are open, or otherwise that there isnoload on the line due to t, and that the butler set is at rest. Currentnow being supplied from the station e will flow by way of the'leads land a to the induction motor I). This will effect gradual starting ofthe rotor of the induction motor I), and the same together 5 with theshaft u, the flywheel a. and the rotor of the commutator machine 0 willgradually accelerate until assuming that there are no turns acting inthe field windings g the rotor is running at Ya speed just below thesynchronous speed. During this starting and acteleration of the bufferset the current in the leads 'n rises momentarily and then graduallyfalls ,to a constant value. Assume now that the load is suddenly ap- 1'5plied at t: The current in the mains l will quickly rise, will draw upthe core 1' because of the-solenoidlc and will thus introduce a certainproportion of the field windings g. \Because of this and because at thistime the shaft to and the rotor d of the machine c'are rotating currentwill be generated by the commutator machine, and in- 1 stead of havingthe effect of a small resistance in series with the secondary winding ofthe induction motor, will, become a source of E. F. opposing the slip E.M. F.

' generated in the secondary winding of the induction motor. This willmean that the net E. M. F. in the circuit including the secondarywinding of the induction motor and the commuted winding ofcthecommutator machine will be diminished, and less current will flowtherein. Considering the induction motor as a transformer, which forthis purpose it can be considered, it will be seen that less currentwill, therefore, be supplied to the primary of the induction motor bythe station \Vith greater loads core a would so move that enough turnsof the 40 field winding 9 would be inserted in circuit that an I). M. F.would be generated in the commuted winding of the commutator machinegreater than the I). M. F. induced in the secondary of the inductionmotor. The

resulting E. M. F. in the. secondary winding will cause a flow ofcurrent in the opposite direction or 180 out of phase with that whichflowed therein during motor action, and cause the asynchronous machine?)to act as a generator delivering current to the system. Again looking onthe induction inotor as a transformer, it will be clear that thenormalsecondary now acts as a primary winding. and the normal primary as thesecondary. whereupon current is delivered to the lines through theleads/n,

and so assists the station in supplying the load demand. This conditionof affairs will obtain until the station can supply the demand or untilthe load is reduced. or until the energy of the flywheel set is.expendcd. It will, therefore, be seen thattheflywheel set acts as abutler between the station and the load, absorbing power at times;absorbing less power at other times and generating power which has beenstored in it at other times, according as the load varies.

It will be understood that because a commutator machine isemployed inthe forms illustrated the frequency of the current which it generates atany instant is e ual to the frequency of the current in its eld coilsand, therefore, the generated current is always of proper frequency toassist or counteract the current supplied to or taken from the secondaryof. the induction motor. \Vhen the induction motor acts as a. generatorthe line will befed by a current of 'proper frequency because thecommutator machine will be excited by current from thesecondary of theinduction motor-of a frequency determined by the slip or, in otherwords, by the line frequency and the speed of the rotor. Just as whenany asynchronous machineis driven above synchronous speed and feedsenergy back to the line, the exciting currents are supplied from theline and the frequency is determined by the line frequency, so here theexciting currents for both the asynchronous machine and the commutatormachine are derived from the line and hence have a frequency such thatthe frequency of the commutator machine and of the asynchronous machineacting as gen erators is correct, regardless of the speed of thefiy-wheel or, of the commutator machine. It will be understood also thatit is not essential to operate the number of acting field coils by arelay or automatic device as is shown, but any suitable means may beemployed, also thenumber of turns acting in the field need not be variedbut any other suitable means may be employed for controlling thecommutator machine as by varying the number of ampere turns acting, orfor rotating the brushes or the like.

I conceive that various modifications of the particular device hereindescribed might be made, and I, accordingly, do not desire to be limitedto the exact arrangement shown and described, but seek to cover in theappended elaims all these modifications which fall within the scope andspirit of my invention.-

Having now described my invention what I claim as new and desire tosecure by .Lettcrs Patent is A buffer set for equalizing the load on asystem of distribution, comprising an asynchronous machine. a dynamoelectric commutator machine, and a fly-wheel. the rotor of saidasynchronous machine being me chanically connected to said fly-wheel,the

primary winding of said asynchronous machine, being electricallyconnected to said s vstei n the secondary winding of said asynchronousmachine being connected in cascade with the commuted winding of saidcommutator machine. and means responsive to the load on said system forvarymg the voltage generated by said commutatey machine in such a mannerthat said asynchronous machine will deliver electrical energy to saidsystem of distribution upon aln increase in the load on said system and"will receive energy therefrom upon a decrease in such load.

In testimony whereof I have hereunto set my hand in presence of twowitnesses.

ARTHUR SCHERBIUS.

\Vitnesses Gno. C. LEBER, A. Linnnicmx'ncn'r.

